Speaker hum problem - need help

I've searched the forums and have seen past posts for this topic, however, I've yet to find an answer that fits my situation.

First, here's my equipment:
Coda CSib integrated amp
Auraliti PK-90 USB server
Dynaudio Focus 380 speakers
Audience Au-24 speaker cables
Cardas Clear XLR interconnects
Cardas Clear & Grover Huffman power cords
Wireworld Platinum Starlight USB

Here's the problem:

With only the amp plugged into power and the speakers connected, I get a 38 db invariant hum coming out of the speakers. The hum does not change no matter what the volume is on the amp. The hum does not change regardless of whether I have the amp plugged into the: wall, a power strip, or a power conditioner. The hum does not change regardless of power cord connected to it. The hum does not change when I plug in the remainder of components and cords into my system.....it is invariant.

I have tried to "lift the ground" with a 3/2 cheater plug, but this had no impact. I sent the amp back to the factory to be checked out and slightly upgraded; they could not reproduce the hum at the factory. A previous amp (tube) produced the same issue, however, with the tube amp, the hum got worse as the volume was raised.

I love the overall sound of this system, but this hum is definitely getting in the way of my enjoyment. Any thoughts out there about what is causing this problem and how to correct this issue?

Many thanks,

Ag insider logo xs@2xmwsl
Nice system.

Have you experimented with the inputs on the amp? How many are there and how many of them are in use? Does the hum change at all when you choose a different source?
Good point Drubin. I wonder if the OP's problem might be helped if he used shorting caps on all of the amp's inputs, except for source inputs that are being used. Almost seems like the amp, through ambient inductance, is picking up a 60 cycle signal at the inputs and the signal is getting amplified. Heck ... maybe he should short all the inputs to see if the problem is ameliorated.

The other alternative is that maybe the OP should fashion a tin foil hat when he listens to his rig. LOL :)

Please report back.

Dan & Bruce, fair points, but the probability that effects at the inputs are causing the problem would seem to be low given that the hum is insensitive to the volume control setting.

Matt, given your thorough (and excellent) description of the issue, I'm mostly stumped. But to grasp at some straws:

1)Perhaps for some reason the AC safety ground pin on the outlet isn't really grounded. It seems conceivable to me that plugging into an ungrounded outlet could cause these symptoms, especially in the case of a high powered amp such as this one.

If you have a multimeter, see if ~120 volts AC can be measured between the smaller of the two vertical slots on the outlet and the metal in the outlet's safety ground opening.

2)Make sure that the speaker cables are not routed close to and in parallel with any power cords. If they are, 60 Hz EMI could conceivably be coupled into the speaker cables, and from there into the amp's feedback loop.

3)Disconnect power from any other components or electrical devices that are close to the amp, although it sounds like you've already tried that.

4)Try turning off any fluorescent lights, compact fluorescent lights, and dimmer switches that are anywhere in the vicinity.

Hope that helps. Regards,
-- Al
Al, ... any thoughts about the tin foil hat idea? :)

@Matt, Al's suggestion to check the ground socket hole is a cheap and quick way to confirm that your socket is properly grounded. If Al's idea is negative, I'd move on to his other suggestions. But if still negative, move on to the next least expensive test.

You said that "[w]ith only the amp plugged into power and the speakers connected," you still get the hum. Does that mean the other source components were also disconnected from the amp? If not, disconnect them.

What Al said about the hum not changing with volume probably eliminates my thought about shorting the inputs, but what the hay, I'd give it a whirl. All you have to do is buy some cheapy shorting caps from Radio Shack.

If still no solution, try borrowing another amp from a friend, or maybe a friendly local dealer. If you're still stuck, try the tin foil hat idea.

Please report back.



Have a great weekend.

I had a problem with my Oppo 105 shedding EMR and being picked up by my turntable's RCA ICs.
This happened with Nordost Blue Heaven (unshielded) and Harmonic Technology Magic (shielded).
The ICs were below the Oppo resulting in 60 Hz hum.
When the Oppo was moved to the side (away from ICs) the
hum stopped completely.
Thanks for all your thoughts, suggestions and quips :-)

So, first, yes, the amp makes this hum with ONLY it plugged in with the speakers connected. All other equipment was disconnected for this experiment. This same hum occurs in two different outlets (which, to be fair, are likely on the same "line" in my house). Each outlet has a different high quality audiophile outlet.

Second, didn't mention this, but prior to purchasing this amp, I auditioned a tube amp, and it too created a hum through the speakers....it, however, got louder when volume was increased. For the Coda amp, the hum "volume" stays the same regardless of output volume on the amp.

Third, I have tried different power cords, and have plugged different power cords into: the power outlet (wall), a high quality power strip, and/or a line conditioner. Nothing has impacted the hum.

Fourth, I am aware of possibility that speaker cables over power cords might create hum and have moved all cables/cords around to no effect (doesn't seem to change anything).

I have not tried shorting the inputs.....thought about it, but not done it yet. Maybe that'll be tomorrow's experiment if i can get to RS before it closes.

Any other ideas would be appreciated.

Maybe I just have exceptionally "dirty" power? If so, would that explain this symptom? And then, what the heck would I do about it?

Thanks again!

Please report back tomorrow after you short the inputs. There's a couple of other switch-outs you can try, but I caution you that if everything else fails ... its the tin foil hat for you.
Do either or both of the upgraded outlets have a small triangle symbol on them, signifying that they are isolated ground types? Did you install the upgraded outlets yourself, or did an electrician install them? Is there a basis for confidence that their safety ground connections are wired correctly?

If you are uncertain as to any of that, while you are at Radio Shack consider purchasing a multimeter, which might help to diagnose any outlet-related issues. Also, consider stopping at a Home Depot-type place and purchasing an extension cord that is long enough to allow you to connect the amp to a different outlet on a different AC run.

Re your other questions and comments, I doubt that "dirty power" could produce this symptom, and I wouldn't assume that the cause of the volume-dependent hum problem with the other amp was the same as the cause of this problem.

Beyond that, the tin foil hat suggestion is probably as good as anything else I can think of :-)

-- Al
Have you tried to move the amp to different location in your house along with the speakers to see if the problem persists ?

Best of Luck

I would double check the outlet wiring--if you don't have one already you can get an outlet checker for about 6 bucks at nearly any hardware or home improvement store. It verifies that hot, neutral, and ground are all correct. If no fault in the wiring of the outlet, I would second the idea of a long extension cord and trying a few other outlets. If nothing else, it rules out a variable. Then I'd swap out speaker cables as the next experiment, again, to rule out a variable. If none of that has a positive outcome. . .then I'm out of ideas, but plenty of smart people here! Good luck.
Try another amp/preamp in your house. It may have really crappy AC outlets with wires just plugged in and old ones can make intermittent contact. Wiggle the plug in the wall and see if the hum changes. Usually a hum equals a ground loop. This is a mystery. Take your Coda to a friends house. If it (coda)works there, and something different in your house doesn't work, your wiring/outlets is suspect. If the Coda hums at a friends, send it to Coda again.
If I were in your shoes, I'd ask my neighbor if I could bring my amp and speakers to his home.

No hum there, you know you have an ac issue at home

If hum there, you know one of two pieces are bad

From there would swap different speaker with same amp, ...you get the picture.
Just a thought - make sure you don't have any halogen lights with variable dimmers turned on while using your equipment. That definitely affects my equipment.
Sounds like many of you are concerned about the "health" of my outlets. The house was brand new in 1990....meaning all new (to code) electrical at that time. I did install both audiophile outlets myself....and know they were done correctly. I do have a halogen cable lighting system installed in the living room, and the transformers live in coves at the top of the walls where the suspect outlets are located. I do, however, have the lighting system completely off when I play music, as I am aware of the noise that the lights add to the system. Is there any chance that the presence of the transformers 8 feet above the outlets might be a cause of this issue....even if the lighting system is turned off? I will start with the extension cord suggestion, and go from there. Thanks to all of you for your suggestions. I'll report back.
Very interesting.
Thank you for your willingness to report your findings back to the forum.
I wish everyone would have such good follow through.
You said that you sent the amp back to the factory and they couldn't find anything wrong with it. Assuming the amp is OK, I would try 2 things. The first would be to connect a different pair of speakers just to rule them out as the problem. If the hum is still there, try the amp in a different location. Maybe in a friends system. That will tell you a lot about what is causing the hum.

One thing you really need to do before making any decisions or spend money is to hear the amp working without the hum. If not, you can't rule it out. The thing you say about the AC being the problem that gives me pause is that you tried different power products and there was no change whatsoever. If your AC is at fault, I would expect you to hear something if you tried different solutions, like a line conditioner. Even if it didn't fix the problem, I would expect to hear some difference; whether it be better, different or worse. I could be wrong, of course, and maybe the AC is the problem, but I would need to hear the amp working properly before I tried fixing anything else.
I just cured a spkr hum problem yesterday! Directly thx to A'gon! A little background 1st. A few years ago I moved from a house to an apt. I set up my system exactly as I did in the house, fired it up and there was a low-level hum/buzz that wasn't present at the house (where it was dead silent). Checked all my connections and plugs and the sound persisted. I've read that apts. often have problems due to 'sharing' (for lack of a better term) the electricity with all the other tenants. I was even using a power conditioner, that I assumed would be an asset (I'm sure some of you are guessing where this is going!;). Cut to a recent thread about power conditioners here on A'gon. Whether or not they hurt or help sonics. I figured I'd check it out just for giggles, I've had my amp plugged into my PC for 7-8 years! Guess what? Not only did I hear an immediate improvement, but the buzz/hum is 100% GONE!! Is this hobby the gift that keeps on giving or what!?;)
Well, I wasn't able to get to RS today (did a nearly 4 hour bike ride in 85 degree heat.....kinda beat), but, I was able to do the extension cord test. Used a (probably) 14 gauge 25 foot Home Depot type extension cord. Tried it in two separate outlets: one across the living room from the outlets I've mentioned, one down the hall. NO CHANGE!

I then tried changing the inputs on the amp (not that I have anything plugged in aside from my XLR and speaker cables), and ran through them all, with each remote outlet (with extension cord attached), and then again with amp plugged into the power strip I've been using. NO CHANGE on any input.

You know.....despite what they said at the factory, I am beginning to wonder about this amp. But, the argument against that was the experience with the previous (tube) amp, with different speakers and cabling. Same hum, except variable based on volume of amp.

I tried one other experiment.....with the amp plugged into it's usual power strip, I tried some other speakers I have in the house....a set of Monitor Audio Silver 7's. Believe it or not.....still heard the same hum!!

I live in a semi-rural neighborhood in the SF Bay Area. There's low density housing and no industry locally. You'd think that would create for some pretty high quality electrical sources? Sounds like I need to buy that outlet checker.

I have contacted the salesperson from the shop at which I purchased the DAC....he said he'd be able to come by this week and try to sort out the situation.

Any other ideas aside from bringing my amp to another location (I could probably do that with the shop at which I bought the DAC)??

This situation is really perplexing and annoying....

Been doing a bit more reading elsewhere......would an "isolation transformer" help in this situation? Is it possible to install one immediately after the wall outlet (i.e., can I plug my power strip into the transformer)? Am I shooting from the hip?
Bad or going bad power supply cap? Would it not do exactly what we hear
Quite a mystery. At this point I can think of only two possibilities, both of which seem very unlikely:

1)The electricians who wired the house when it was built messed up big time, perhaps leaving a safety ground run unconnected, or even reversing the hot and neutral runs, such that all of the outlets you've tried were affected.

2)Or (as Bill/Grannyring suggested) the amp has a bad filter capacitor or other issue, which Coda was negligent in not detecting when you sent it back to them.

Regarding your question about an isolation transformer, I see no reason to expect that to help.

-- Al
"I then tried changing the inputs on the amp (not that I have anything plugged in aside from my XLR and speaker cables), and ran through them all, with each remote outlet (with extension cord attached), and then again with amp plugged into the power strip I've been using. NO CHANGE on any input."

Just to be clear, when you were swapping out components, did you leave the IC's plugged into the amp? Because if you left them in the amp but not connected to anything on the other end, that can produce a hum like you are describing. Especially if open ends happen to be touching something. Also, does the amp have a way to go back and forth between balanced and single ended operation? Having that on the wrong setting can also cause a hum if its not in the right mode. Last, if the amp allows you to adjust the level of each input individually, along with a global volume control, try reducing the level on the individual input.
If you look at my two systems listed on Audiogon you will notice that my power filtration system uses two Isolation Transformers 5 KVA/each into my subpanal which feeds all my audio outlets. Although you could set an isolation transformer different then I did, and plug the isolation transformer into you audio outlet and then components into the isolation transformer I can almost garentee (99% sure) that it will not help your situation as Al mentioned. It can however clean most of the grung from your AC line but I don't think that's creating you problem. After reading all that has been posted in this forum, I think your amp is the culprit.
Mwsl, picking up on Zd542's suggestion. If your integrated amp has both XLR and SE input capability, can you use a shorting shunt on unused XLR inputs?

I had a hum problem with my former ARC power amp, which had both XLR and SE inputs. I'd get a hum if I used the SE inputs and forgot to shunt the XLR inputs.

Other than that, I think Zd542 and Al are leaving you with the best straws to grasp at for now. I gotta say that if your amp was checked out by Coda and they missed bad power supply or coupling caps, I'd be extremely surprised. But, as Forrest Gump said, "sh*t happens."

Please let us know how you make out, especially if the dealer comes out.


I was able to do the extension cord test. Used a (probably) 14 gauge 25 foot Home Depot type extension cord. Tried it in two separate outlets: one across the living room from the outlets I've mentioned, one down the hall. NO CHANGE!
This test is not exactly like Al recommended,
an extension cord that is long enough to allow you to connect the amp to a different outlet on a different AC run.
The important part is "different AC run." "One across the living room" is likely the same run as any outlet in the living room. "One down the hall" may also be on the same run as the living room. The only way to know is to turn off the breaker for the living room, and see if the hall outlet still has power.

I don't think there is any doubt that this is either an amp issue or house wiring issue(just living room or maybe whole house).

IMHO, the best plan of action would be to take the amp to the hi-fi shop you mentioned, then if it works OK there, you know it is your house. Then try the amp in another room of your house, preferably as far from the living room as you can and if it works OK, it's the living room, or if it hums, then the whole house.

You could try a different room in your house first, but if it hums, then you must take the amp to the hi-fi shop for testing.

Good Luck
Thanks for the additional suggestions upon which to follow up. Given that it's a holiday weekend, nothing will happen with the dealer until next week.

The outlet in the hallway is definitely a different circuit than the ones in the living room. I am aware of that from previous adventures in turning off circuits :-)

I'll follow up here in the next few days. I guess I'm coming to the hypothesis that there's something amiss with the electricity in my living room.

Thanks again for all the great input.

Question: In addition to the hum emanating from the speakers, is there ALSO a hum or buzz coming directly from the amplifier?

-- Al
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Al - there is no hum coming from the amp itself.

Mental - I have already tried the experiment of disconnecting everything from the amp aside from speakers cables and the power cord. I get the hum just with that minimal set of "items" plugged in.


Do you have an AM/FM radio you could plug into the same mains power receptacle as the Coda amp? If so set the tuner to an AM station and listen for the hum/buzz.

If the radio sounds ok then I would think the problem is not AC mains power related but rather a problem with the Coda amp.
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Here's another thought that happened to me several years ago that I almost forgot about. I had a similar problem and the cause was a loose ground wire in the main circuit panel.
Although it looked like all the ground wires were sercure, I traced the wiring for the outlet and where the ground wire was connected in the panel. Everything looked good but sure enough the group of ground wires needed to be repositioned and the screw bolt retightened. The hum stopped. You might want to check that out if the amp tests goos at another location.
LAK - very interesting possibility. There's been lots of work in our panel over the years. i will try to check it out!
Matt, Whats up with the Hum?
Do you have an opportunity to try your amp at another location?
Will have updates later this week. Am meeting with a fellow Audiogon'r on Thursday, and the dealer on Friday.
Went over to fellow Audiogoner drubin earlier today (thanks Dan!!) to try my amp in his system. Had the same exact problem occur in his system that I do in mine; hum coming through speakers when as little as (any) power cord and speaker cables are plugged in. He heard it too!!

Looks like my amp has a problem. I just contacted Coda and am waiting for a response. Odd that they claimed to have not heard it when it was at the factory less than a month ago. This time, I'll bring it in myself, and make sure that I have someone there listen to it with me. Fortunately, they're only about an hour away.

(As a complete aside.....I almost bought a highly regarded integrated from a european manufacturer before I purchased the Coda. They were offering a screaming deal (I know it was legit). I kept on musing about "if there are any problems with this, how am I going to get this fixed?" Glad I listened to that little inner voice and bought domestically (and, locally, as it turned out).

I'll keep you apprised as this saga continues. Kudos to those that thought it was an amp problem all along. You get extra points for that call :-)

Power supply cap:-) been there, done that and your comments point
straight to it. I would be most surprised if it was anything else. Can't say
with 100% certainty, but perhaps 80% certainty!
I got a response from Coda within 2 hours. They want the amp back at the factory, and will pay for shipping both directions. They verified that they had listened to the amp through their speakers, and could not hear the hum.

The hum is stable at about 37 db, and is audible in my listening position 9 feet away from the speakers when there are quiet passages in the music (or when no music is playing). Is this level of hum normal in quality sound systems?
Jim (Jea-48) - just curious if you could say more about what/how to do the AM radio experiment. Should I actually tune into a station......or just set it to the very beginning or end of the band? What am I listening for if I set it to the station....I have very poor reception around here as I'm in a very hilly location?

Just curious about this suggestion.

"06-06-14: Mwsl
I got a response from Coda within 2 hours. They want the amp back at the factory, and will pay for shipping both directions. They verified that they had listened to the amp through their speakers, and could not hear the hum."

I think that's good news. Fixing the problem at no cost to you is the best solution. I suspect that when they had your amp the first time, they were just careless. They probably tested it to see if it worked, but didn't do any critical listening. Yes, that's not good, but I think you'll get your amp back working properly.
Zd and Mwsl ... yes that's good news indeed. Not sure how to put this, so please do not take it as me being snippy.

Mwsl's unfortuante experience is one of the reasons why I love ARC. My personal experience is also consistent with what I have read on ARC's web site and in various audio articles. Specifically, no unit leaves ARC's shipping dock (new or repaired) until William Gehl, ARC's offical live tester, plugs the unit into a system gives it a good listen. Mr. Gehl initials a QC card which accompanies the unit, and only then is the unit shipped out. Every ARC unit I own or have owned has a QC card with his initials. Mr. Gehl must have an incredible auditory memory.

Is the systen perfect? Does a chicken have lips? Same answer .... after all, it's run by human beings.

Anyway ... I sincerely hope that Coda puts your amp back in 100% operating condition and this is the end of your aggravation.


Jim (Jea-48) - just curious if you could say more about what/how to do the AM radio experiment. Should I actually tune into a station......or just set it to the very beginning or end of the band? What am I listening for if I set it to the station....I have very poor reception around here as I'm in a very hilly location?

Just curious about this suggestion.
06-06-14: Mwsl

Earlier in one of your posts you said you tried a ground cheater on the AC power plug of the amp. Doing so ruled out the safety equipment ground being the problem.

If by chance somewhere in the 120V circuit that is feeding the amp there is a loose and or corroded connection, that could possibly cause an RFI interference in the amp and cause a buzz heard through the speakers. If there is a loose and or corroded connection an AM radio plugged into the same receptacle as the amp could/would cause a buzzing sound in the speaker of the radio because of the RFI interference being generated.

As for the AM station used, set the tuner on a moderate signal strength station. No buzz, then try a weaker AM station.

Like others have said in this thread, the problem is more than likely the amp.
I had an opportunity today to go to a local audio store. Brought in the integrated, thinking, if I can still hear the hum, and the staff can hear it, then we've isolated the problem. And, fortunately, the problem remained, obvious to all ears. It was interesting to me that after listening to my integrated hum away, the salesperson plugged in a $1000 integrated into the exact same cords, cables and connects......and all I heard was a blissful silence. For those of you who thought my amp was problematic, you are correct. Alas, I'm still waiting for the word from CODA for when they'll be ready to receive my amp for repair; the owner/founder has been out due to a severe injury, so I'm biding my time waiting for his return.
Thanks for the update, I wondered what was happening.
When you get the issue resolved please let us know what needed to be replaced.
After much delay, I finally got my problem resolved.....and quite nicely!

Doug Dale, the owner of Coda, had been severely injured many months ago and has been off work until last week. Much of the delay that I experienced was due to Doug's absence. He was apologetic for the delay.

As soon as he got back to work, he decided to simply swap out my unit for a new one that he had tested and was sure worked to spec....with no noise. I brought my amp in today. We listened to it in his listening room and (thankfully) heard the noise....although it was MUCH quieter in his room with his Legacy speakers that it was in my room with my speakers. We then listened to the new amp that he had selected to replace mine.....it wasn't dead quiet, but the noise was of a much less obtrusive nature that he said was normal and (I believe) related to the volume control used.

I brought the amp back to my house, plugged it in and......it's lovely...no noise. Again, not dead quiet, but WAY more quiet than my previous unit. Since the replacement unit is new I'll have to break it in again, but, frankly, that's not that bad a prospect :-)

Doug did say that very infrequently, generally due to shipping issues (dropping, rough treatment) some wires get slightly loose and may cause the issue I have been having. Oh well, just bad luck on my part.

It was cool seeing the Coda facility.....there's only 4 employees (that I saw) including Doug, so it's a small operation. But they're producing some neat products.

OK, I'll check back in in a few weeks....but I'm VERY heartened with today's news. Thanks again to all of you for your support and help.